1. Field of the Invention
The present invention relates to an information processing apparatus for recording and/or reproducing information utilizing a physical interaction (tunnel current, interatomic force, etc.) occurring when a probe is put near a recording medium.
2. Related Background Art
In recent years, applications of memory materials are the core of electronics industries including computers and equipment related thereto, video disks, digital audio disks, and so on, and development of suitable material is very active.
The performance required for memory materials differs depending upon their applications, and quick response speeds of recording and reproduction are necessary and indispensable.
Conventional memories were mainly semiconductor memories and magnetic memories using materials such as magnetic materials and semiconductor materials, but the recent progress of laser technology has brought cheap and high-density recording media by optical memories using an organic thin film of an organic dye, a photopolymer, or the like.
On the other hand, recently developed was the scanning tunneling microscope (hereinafter abbreviated as "STM") capable of directly observing the electron structure of surface atoms of a conductor [Binnig et al., Phys. Rev. Lett., 49, 57 (1982)], which enabled high-resolution measurement of real space image for any single-crystal and amorphous materials and which had an advantage of capability of observing a sample at low electric power without damaging the sample by an electric current. In addition, the scanning tunneling microscope operates even in the atmosphere and can be used for a variety of materials, and applications thereof in a wide range are thus expected.
The STM utilizes a phenomenon that a tunnel current flows when a metal probe (probe electrode) is brought to the proximity of an electroconductive substance, approximately up to the distance of 1 nm, while a voltage is applied between the metal probe and the electroconductive substance.
This electric current is so sensitive as to respond exponentially to a change of distance between the two elements. When the probe scans so as to keep the tunnel current constant, it is also possible to read a variety of information concerning the total electron cloud in the real space.
The resolution in the in-plane direction achieved by this technique is approximately 0.1 nm. It is thus fairly possible to achieve high-density recording and/or reproduction on the order of atomic scale (i.e., on the subnanometer order) by applying the principle of the STM.
For example, the information processing apparatus disclosed in the bulletin of Japanese Laid-Open Patent Application No. 61-80536 is arranged to write information by removing atomic particles that have been absorbed on a surface of a medium by means of an electron beam or the like and to reproduce the data by an STM.
There is a proposed method for using a thin film layer of a material having a memory effect for voltage-current switching characteristics, for example a thin film layers of organic compound having a conjugated .pi. electron system or a chalcogenides, as a recording layer and performing recording and/or reproduction by means of an STM (Japanese Laid-open Patent Applications No. 63-161552 and No. 63-161553). This method can achieve bulk recording and/or reproduction of even 1 Tbit/cm, supposing that the bit size recorded is 10 nm.
An example for a scanning mechanism of the probe electrode is a cantilever type (Japanese Laid-Open Patent Application No. 62-281138), and, according thereto, a plurality of cantilever mechanisms of SiO.sub.2 can be made in the size of approximately the length 100 p.mu., the width 10 to 20 .mu.m, and the thickness 0.5 .mu.m on an Si substrate, and writing and reading circuits are also integrated on the same substrate.
Such bulk memory systems are useful for processing image data, including, especially, very large amounts of information as database of large information amounts).
For example, they are indispensable for high-definition televisions, high-resolution still video systems, and so on, recently showing extreme progress of technology.
In such bulk memory systems, however, if input information is always read out at a constant resolution of high definition, or at a detailed level, reading will require a lot of time and will be often wasted.
Specifically, it is the present status that the memory systems as described above require a lot of time for writing or reading of large amounts of information because the scanning frequency limit, due to the physical condition of resonance frequency of cantilever or the like, is several hundred Hz and the limit on the transfer rate of information per probe caused thereby is several hundred kHz or less. In addition, detailed information and high definition resolutions are not always necessary, depending upon the purpose of output in a given instance, the output device in question, or the like. For example, in the cases of searching, access to data head, and the like, priority is given to processing speed over quality of image. In addition, for example, in a case of the still video system or the like, a high resolution is necessary when an image is printed out by the electrophotographic technology or the like; however, a monitor output does not require such a high resolution. Therefore, it is not always necessary to read out hundred percent of the information recorded.
Also in the case of recording, when only a necessary part is desired to be recorded in detail or when speed is important, we may employ a method of input of data arranged to record data first roughly and to locally supplement necessary portions in detail later.